A stenosis, or narrowing of a blood vessel such as an artery may comprise a hard, calcified substance and/or a softer thrombus (clot) material. There have been numerous therapeutic procedures developed for the treatment of stenosis in an artery. One of the better-known procedures is percutaneous transluminal coronary angioplasty (PTCA). According to this procedure, the narrowing in the coronary artery can be reduced by positioning a dilatation balloon across the stenosis and inflating the balloon to re-establish acceptable blood flow through the artery. Additional therapeutic procedures may include stent deployment, atherectomy, and thrombectomy, which are well known and have proven effective in the treatment of such stenotic lesions. Distal occlusion or filtration, with or without aspiration embolectomy, have also been developed as adjunctive procedures to prevent downstream embolization by collecting and removing atheroembolic debris that may be generated during any of the above therapies. Increasingly specialized aspiration catheters have been developed for aspiration of body fluids contaminated with thrombus or embolic debris before, during and/or after an arterial intervention.
The therapeutic procedure typically starts with the introduction of a guiding catheter into the cardiovascular system from a convenient vascular access location, such as through the femoral artery in the groin area or other locations in the arm or neck. The guiding catheter is advanced through the arteries until its distal end is subselectively located in a branch vessel leading to the stenosis that is targeted for treatment. During PTCA, for example, the distal end of the guiding catheter is typically inserted only into the origin of a native or bypass graft coronary artery. A guidewire is advanced through a central bore in the guiding catheter and positioned across the stenosis. An interventional therapy device, such as a balloon dilatation catheter, is then slid over the guidewire until the dilatation balloon is properly positioned across the stenosis. The balloon is inflated to dilate the artery. To help prevent the artery from re-closing, a physician can implant a stent inside the artery. The stent is usually delivered to the artery in a compressed shape on a stent delivery catheter and expanded by a balloon for implantation against the dilated arterial wall. Prior to the insertion and use of the interventional therapy catheter, an aspiration catheter may be advanced over the guidewire and used to suction thrombus that may be clinging to the stenosis. An aspiration catheter can also be used following the therapy catheter to remove contaminated blood that has been held close to the treatment area by temporary occlusion or filtration devices.
In order for the physician to direct the guiding catheter and/or aspiration catheter to the correct location in the vessel, the physician must apply longitudinal forces, and sometimes apply rotational forces. For the catheter to transmit these forces from the proximal end to the distal end, the catheter must be rigid enough to be pushed through the blood vessel, a property sometimes called pushability, but yet flexible enough to navigate the bends in the blood vessel. The catheter may also require sufficient torsional stiffness to transmit the applied torque, a property sometimes called torqueability. To accomplish this balance between longitudinal rigidity, torsional stiffness, and flexibility, there is often a support member added to the catheter shaft. This support member is often comprised of a woven reinforcement or coiled filament embedded in the shaft. This support wire is often embedded between two adherent layers of tubing to form a composite laminated catheter shaft.
Using the femoral artery approach in a PTCA procedure, a catheter is passed upward through the aorta, over the aortic arch, and down to the coronary artery to be treated. It is preferable the guiding catheter or aspiration catheter have a soft tip or flexible section for atraumatically passing through the selected vessels. Therefore, it is advantageous to have the proximal section be rigid to transmit the applied forces, but to have a distal section be more flexible to allow for better placement of the catheter distal section within tortuous vasculature. The need for this combination of performance features makes it desirable for a catheter shaft to have variable flexibility along the length of the catheter. More specifically, it is desirable for a catheter to have increased flexibility near the distal end of the catheter shaft and greater stiffness near the proximal end.
One approach used to balance the need for pushability and torqueability while maintaining adequate flexibility has been to manufacture a catheter that has two or more discrete tubular portions over its length, each having different performance characteristics. For example, a relatively flexible distal section may be connected to a relatively rigid proximal section. When a catheter is formed from two or more discrete tubular members, it is often necessary to form a bond between the distal end of one tubular member and the proximal end of another tubular member. This method requires substantial manufacturing steps to assemble the various sections and makes it difficult to manufacture the entire catheter shaft utilizing low-cost coextrusion technology. Further, such a shaft design may include relatively abrupt changes in flexibility at locations where material changes occur. Besides being cumbersome to manufacture, a catheter with abrupt changes in flexibility may be susceptible to kinking at such stress concentrations.
Various other approaches for achieving variable stiffness of the catheter shaft include varying the braid pitch of the reinforcement layer and/or varying the properties of materials used in construction, such as by removing a selected distal portion of an outer tubular layer of the catheter shaft and replacing that distal portion with one or more sections of more flexible tubing. A unitary catheter shaft arrangement with variable stiffness is also known that incorporates one or more layers of a material that is curable by ultraviolet light, wherein selected portions of the catheter shaft are subjected to radiation to cure, the material and thereby increase the stiffness of the shaft in the treated area. Another catheter having variable stiffness is taught in U.S. Patent Application Publication No. U.S. 2004/0225278 A1 to Poole, et al. The Poole, et al. publication teaches a catheter having varying stiffness achieved by making lamination bonds of varying integrity between a liner and an outer shell.
However, a need still exists for guiding catheter shafts that can be easily manufactured, such as by continuous extrusion, co-extrusion and/or other reel-to-reel processes, and have a variable stiffness without assembling multiple components of the shaft or attending to difficulties inherent in irradiated variable-stiffness catheters, such as the limitations in the choice of catheter materials and in the control of the final catheter properties.